How to start a game when all players are in

Here is the problem:
In my game all the players choose a character and then they're moved in a "waiting room".
I would like to start the game when 4 player are in.
But if i use gms_other_count or gms_session_player_count or gms_info_isloggedin or instance_number, the game starts while the fourth player is in the "choose character room".